1. Field of the Invention
The present invention relates to an ultrasonic diagnostic device and, more particularly to an ultrasonic diagnostic device which can display a tomographic image or a three-dimensional image of a specific region from information obtained by scanning a living body; further to an ultrasonic diagnostic device which can offer an accurate two-dimensional or three-dimensional image by synthesizing a plurality of tomographic image signals having different positions or directions.
2. Description of the Prior Arts
There is a well-known ultrasonic diagnostic device in which the surface of a living body is irradiated with ultrasonic waves for observing the inner part of the living body and a tomographic image of the living body or an image on a sectional plane which makes a right angle with the scanning sectional plane in a three-dimensional meaning is obtained by detecting the reflected waves from the living body. Among the devices of this kind, as shown in FIG. 7, a probe P is scanned in an X axis direction for a living body, and the obtained tomographic image signal of an X-Z cross section S is stored in an image memory, and then the probe P is moved by a specified small distance .DELTA.Y in a Y axis direction and the probe is again scanned in the X axis direction and another tomographic image signal is obtained in the similar way as mentioned in the above. If a plurality of these two-dimensional tomographic image signals obtained by repeating the process described in the above are transformed to the signals on three-dimensional coordinates, they, as a whole, form a signal showing a three-dimensional image; therefore it is possible to display a tomographic image taken along an arbitrary cross section as shown in FIG. 8. (See Japanese Laid-open Patent Publication No. Sho 56-70757.)
In this kind of devices, a probe is scanned only once in a specific region (hereinafter referred to as a watch point), so that only one image signal is obtained for a watch point. Ultrasonic waves, in their nature, are strongly reflected by a hard tissue like a bone and also permeate diffracting around it; therefore, when there is a tissue which reflects ultrasonic waves in the vicinity of a watch point, a complete image is not always obtained.